Bachtobelstrasse goes from Uetlibergstrasse to Kolbenhofstrasse. It is named after the ravine (Tobel) next to the Kolbenhofbach (stream leading to the Sihl river).
The Kolbenhofbach in question
The 3-story building in the back is a school building (probably an extension of an existing school); there are a lot of these prefab buildings around the city (I just learnt they're called Züri-Modular)
The city is checking that nobody's stealing the stream. (More probably it measures the amount of water, though.)